1. Field of the Invention
The present invention relates to a hollow-molding method and a molding apparatus for conducting the same method and a container manufactured by the same method, and particularly to a plastics container provided with a projection generally called "chime" in its top portion, and a method and an apparatus for molding the same container, which chime has a predetermined configuration with predetermined width and height.
2. Description of the Prior Art
In a plastics container, particularly, in a large-size one of a capacity of 50 to 200 l in volume, there is provided a projection, for example such as an annular flange, having a predetermined configuration with predetermined width and height in order to facilitate handling and shipping which is generally called "chime". It is generally preferable that the chime is wider in its width and higher in its height.
Hitherto, in a conventional method for forming the chime, the chime is manufactured according to the actuator process. However, in such conventional method, the following problems exist:
(I) it is difficult to obtain a good timing for moving a mold;
(II) restrictions on the width and the height of the chime exist;
(III) operation of the mold is complex; and
(IV) in case that a plastics having a good fluidity is employed, such a material is apt to drip in molding operation of a container so that a biased wall thickness is apt to be produced in such molded container.
Further, another conventional molding method and apparatus have been proposed in Japanese patent application No. 207101/1984 filed by the applicant of the present application, which conventional apparatus is shown in FIG. 2, wherein: the reference numeral 1 designates a die for extruding molten resin; the numeral 2 designates a lower mold with a concave portion 2a which has a predetermined configuration and predetermined width and height; the numeral 3 designates a lift cylinder for performing an up-and-down movement of the lower mold 2; the numeral 4 designates an air nozzle provided in the lift cylinder 3; the numerals 5A and 5B designate a pair of opposite side molds; the numerals 6A and 6B designate a pair of opposite cylinders for moving the opposite side molds 5A and 5B; the numeral 7 designates a hole for passing heated steam or cooling water; and the numeral 8 designates a cooling water hole. All of the inner surfaces of the lower mold 2, and the opposite side molds 5A and 5B and the lower surface of the die 1 are coated with fluorine containing resin. Incidentally, a notch portion 1a is formed in a peripheral portion of the the die 1, in which notch portion 1a the lower mold 2 is inserted. On the other hand, for facilitating an operation of a drum handling machine in shipping, as shown in FIG. 5 the chime "A" is provided with a projecting portion A1 in its lower outer periphery. Due to such provision of the projecting portion A1, an outside ring portion of the concave portion 2a of the lower mold 2 is formed into a separate split mold, i.e., a chime ring B which is provided with a notch portion B1 corresponding to the projecting portion A1, to make it possible that the chime ring B is separated from the chime when the molding operation of the product is completed.
On the other hand, in such apparatus, after the lower mold 2 is lifted so that the lower mold 2 is brought into a press contact with the die 1 to form a top portion of the plastics container, the lower mold 2 is lowered to perform a parting operation of the plastics product. At this time, since the molten resin received in the chime A portion swells again so that the chime ring B is pushed up in the notch portion B1 thereof, the chime ring B is lifted. Consequently, the top portion of the chime ring B projects upward beyond the predetermined level when the lower mold 2 is lowered to a predetermined position. As a result, at a time when the side molds 5A, 5B are closed, such side molds 5A, 5B interfere with the chime ring B to jam the same while the projecting portion A1 varies in its width. Consequently, in the conventional molding apparatus, the parting operation of the lower mold 2 constitutes one step in the molding operation to extend a necessary molding time and to make it difficult to automate the molding operation.
Further, in the molding operation of the plastics container by means of the conventional blow-molding apparatus, there is a tendency to produce a V-shaped notch N in its pinch-off portion as shown in FIG. 15D to decrease impact strength of the molded product in drop and to make it easy that the molded product is exfoliated. These are problems inherent in the conventional molding method and apparatus.
In order to resolve the above problems, it is possible to modify the pinch-off portion of the mold in its configuration and to modify the molding conditions, particularly to decrease a mold-clamping speed, so that it is possible to improve the pinch-off portion to the extent of a condition shown in FIG. 15E. However, such improvement is not sufficient, while the decrease in the mold-clamping speed leads to a poor operativity. The inventor of the present invention has found that a cooling speed of the parison in the prior art causes the above problems, from various researches.
On the other hand, as the drum becomes larger in size, the drum needs to be mechanically transferred, stacked and stored, by means of a special handling machine, for example such as a drum handling machine. Consequently, it is necessary to make it possible that the drum is easily and surely clamped by the handling machine and detached easily and surely therefrom. However, the drum molded by the conventional method and apparatus has the following problems:
(1) it is difficult to grasp the chime of the drum by the handling machine;
(2) the ground plate of the drum is substantially similar in diameter to the top portion of the same drum to make it difficult to stack the drums into neat piles;
(3) since in a falling down condition the drum contacts the ground in its whole trunk, it is difficult to change its rolling direction; and
(4) since the up and down sides of the drum are not changed, the bottom surface of the ground plate is always subjected to a load, while since the pinch-off portion is formed in the bottom surface of the ground plate in a lateral straight line manner, the ground plate lacks rigidity in the bottom surface thereof.